C++ Data Types, Sizes and Value Ranges: Complete 64-Bit Memory Matrix

Every value stored in a computer's memory must have a clearly defined Data Type. The data type instructs the compiler how many bytes of RAM to reserve and how to interpret the binary bit patterns stored inside.

C++ Data Types Sizes and Value Ranges Matrix

Figure 4: Complete C++ Data Types and Memory Footprint Matrix

Classification of C++ Data Types

Primitive / Built-in Types: int, char, float, double, bool, void.
Derived Types: Arrays, Pointers, References, Functions.
User-Defined Types: struct, class, union, enum, typedef / using.

Complete Primitive Types & Sizes Reference

Data Type	Size (Bytes)	Bits	Approximate Value Range	Typical Real-World Use Case
`bool`	1	8	`true` (1) or `false` (0)	Flags, logic conditionals
`char`	1	8	-128 to 127 (or 0 to 255 unsigned)	Single ASCII character (`'A'`)
`short`	2	16	-32,768 to 32,767	Small numbers, audio samples
`int`	4	32	-2.14 Billion to +2.14 Billion	General-purpose counters, loop indices
`unsigned int`	4	32	0 to 4,294,967,295 (~4.29 Billion)	Quantities that cannot be negative (sizes)
`long long`	8	64	-(2^63) to 2^63 - 1 (~9 Quintillion)	Large IDs, database keys, high-precision time
`float`	4	32	~1.18e-38 to 3.40e+38 (7 digits precision)	Graphics shaders, physics engines
`double`	8	64	~2.23e-308 to 1.79e+308 (15-17 digits)	Scientific simulations, financial math

Practical Example: Verifying Sizes with `sizeof`

#include <iostream>

int main() {
    std::cout << "Size of bool:      " << sizeof(bool) << " byte\n";
    std::cout << "Size of char:      " << sizeof(char) << " byte\n";
    std::cout << "Size of int:       " << sizeof(int) << " bytes\n";
    std::cout << "Size of long long: " << sizeof(long long) << " bytes\n";
    std::cout << "Size of double:    " << sizeof(double) << " bytes\n";
    return 0;
}

Frequently Asked Questions (FAQ) - Student & Interview Review

Q1. What is the size of an int in C++ on 64-bit systems?

Under the standard LP64 and LLP64 data models used by 64-bit Windows and Linux systems, a standard 'int' is 4 bytes (32 bits), holding values from -2,147,483,648 to 2,147,483,647.

Q2. What is the difference between float and double in C++?

A float occupies 4 bytes and provides single precision (~7 decimal digits of accuracy). A double occupies 8 bytes and provides double precision (~15 to 17 decimal digits of accuracy). Modern CPUs handle double calculations at nearly identical speed, making double the industry default.